This invention relates to a process for the production of an indicator for monitoring the temperature of a cooled or deep-frozen product, such as packaged foodstuffs, pharmaceuticals and the like, the indicator indicating that a critial temperature of the cooled or deep-frozen product has been exceeded, as well as a novel method of using the indicator in accordance with the invention. To this end, "cooled products" are products which should be cooled to a temperature exceeding 0.degree. Centigrade, whereas "deep-frozen foodstuffs" are constantly and uninterruptedly kept below a critical temperature of about -17.degree. C.
Even a brief heating and a repeated cooling or freezing may lead to serious deleterious changes to the foodstuffs, which frequently cause serious damage to health. This applies similarly to pharmaceuticals, preserved blood and other products.
A strict monitoring of the "cooling chain" is necessary, primarily in the case of industrial cooling or freezing until the defrosting operation prior to consumption of the foodstuffs occurs.
Unfortunately, however, technical breakdowns, and also human failure, can never be wholly prevented. An object of the invention is to specify a process which permits uninterrupted verification that the specified critical temperatures has actually never been exceeded.
Until now, a monitoring operation on such cooled or deep-frozen products was possible only with difficulty. Thermometers utilising following pointers were commonly utilised for this purpose, wherein it was then possible to detect that the critical temperature had been exceeded to the point of thawing of the cooled or deep-frozen product, based on the position of the trailing pointer. On the one hand, thermometers of this kind are comparatively costly, and on the other hand, are easily manipulated.